Better math import from PPTX into Impress

Impress now has a much improved math handling in its importer from PPTX, eliminating annoying duplicated objects you had to delete after import, manually.

First, thanks TU Dresden who made this work by Collabora possible.

Here is how it looks:

What you can see is that the in the old case we managed to read both the actual math object and its replacement image from PPTX, which caused visible duplication due to working transparency handling. The new way just imports the math objects, and ignores the replacement graphic.

This new way (handling of the OOXML a14 feature flag) is enabled by default, except for Calc documents, where more works is needed before it can be enabled.

All this is available in LibreOffice master (towards 6.4), so you can try it out right now, if interested.